Dip angle and direction of a plane described by 3 points

I'm trying to make a model in excel which calculates the dip angle
and direction (azimuth or bearing) of a plane descriped by 3 points in a coordinate
system.
The planned use is a quick-look geomodel where I would like to
calculate formation dip based on the observation of a specific
geological feature in three separate wells. The points where the
well intersects the formation in each well is described by a UTM
latitude/longitude and depth below a fixed datum. Point 1 (x1, y1,
z1), point 2 (x2, y2, z2), point 3 (x3,y3, z3).
By definition, the dip angle is perpendicular to the strike (a
horizontal line through the plane) 0 degrees meaning a horizontal
plane/90 degrees meaning a vertical plane, and the dip azimuth is
the compass direction/bearing of the dip angle.